cron jobs running several seconds after scheduled

mathison · #1 August 31st, 2010, 17:26

Greetings,

I have a basically clean install of FreeBSD 8.1 stable (i386) running under as a virtual machine on an ESX host.

uname:

Code:

FreeBSD NetRouter 8.1-STABLE FreeBSD 8.1-STABLE #0: Thu Aug 19 09:37:22 EDT 2010 /usr/obj/usr/src/sys/NETROUTER  i386

The kernel was recompiled using the kernel config shown below.
Also, several sysctls parameters were adjusted as shown below.

The cron daemon is running only with the -s flag, (though I did specify -J0 to see if it had any effect - it did not.)

The issue I am having are that cron jobs are not executing until 10 seconds or later after 'scheduled'. The pattern is consistent regardless of the time of day, load, etc. Though I realize that cron is only accurate to the minute - meaning the task is only expected to run sometime in the scheduled minute (0-59 seconds), my other FreeBSD servers all seem to run these tasks at the 0 second, with no multi-second delays.

What should I be looking into to determine what is so different with this installation that it would insert 10 seconds or more of delay in the cron processing chain? [I did enable several debug flags on the cron daemon, hoping to see what was happening in those first ten seconds, but that did not enlighten me.]

Thanks for any pointers.
Neil

/var/log/cron:

Code:

Aug 31 06:30:10 NetRouter /usr/sbin/cron[44544]: (root) CMD (/usr/libexec/atrun)
Aug 31 06:33:10 NetRouter /usr/sbin/cron[44546]: (operator) CMD (/usr/libexec/save-entropy)
Aug 31 06:35:10 NetRouter /usr/sbin/cron[44558]: (root) CMD (/usr/libexec/atrun)
Aug 31 06:40:11 NetRouter /usr/sbin/cron[44562]: (root) CMD (/usr/libexec/atrun)

sysctl.conf:

Code:

kern.ipc.somaxconn=1024

# polling tuneables
kern.polling.burst_max=1000
kern.polling.idle_poll=0
kern.polling.each_burst=50

# network tuneables
# -----------------
# maximum segment size (1500 bytes - 40 header bytes)
net.inet.tcp.mssdflt=1460
# use an even multiple of MSS (78840/1460 = 54)
net.inet.tcp.recvspace=78840
net.inet.tcp.sendspace=78840
# 54 packets fit into 78840 bytes
net.inet.tcp.slowstart_flightsize=54

# turn on tcp delayed ACK - increases likelyhood that the first response will
# have first ACK piggybacked
net.inet.tcp.delayed_ack=1
net.inet.tcp.delacktime=100

# enable tcp inflight (using manpage recommendations)
net.inet.tcp.inflight.enable=1
net.inet.tcp.inflight.min=6144

# loopback tuning
net.local.stream.sendspace=82320
net.local.stream.recvspace=82320
net.inet.tcp.local_slowstart_flightsize=10
net.inet.tcp.nolocaltimewait=1

# host cache
net.inet.tcp.hostcache.expire=1

Kernel config file:

Code:

cpu I686_CPU                                                                             
ident NETROUTER                                                                       

makeoptions     DEBUG=-g                # Build kernel with gdb(1) debug symbols

options         SCHED_ULE               # ULE scheduler
options         PREEMPTION              # Enable kernel thread preemption
options         INET                    # InterNETworking                
options         SCTP                    # Stream Control Transmission Protocol
options         FFS                     # Berkeley Fast Filesystem            
options         SOFTUPDATES             # Enable FFS soft updates support     
options         UFS_ACL                 # Support for access control lists    
options         UFS_DIRHASH             # Improve performance on big directories
options         UFS_GJOURNAL            # Enable gjournal-based UFS journaling  
options         MD_ROOT                 # MD is a potential root device         
options         NFSCLIENT               # Network Filesystem Client             
options         NFSSERVER               # Network Filesystem Server             
options         NFSLOCKD                # Network Lock Manager                  
options         NFS_ROOT                # NFS usable as /, requires NFSCLIENT   
options         MSDOSFS                 # MSDOS Filesystem                      
options         CD9660                  # ISO 9660 Filesystem                   
options         PROCFS                  # Process filesystem (requires PSEUDOFS)
options         PSEUDOFS                # Pseudo-filesystem framework           
options         GEOM_PART_GPT           # GUID Partition Tables.                
options         GEOM_LABEL              # Provides labelization                 
options         COMPAT_43TTY            # BSD 4.3 TTY compat (sgtty)            
options         COMPAT_FREEBSD4         # Compatible with FreeBSD4              
options         COMPAT_FREEBSD5         # Compatible with FreeBSD5              
options         COMPAT_FREEBSD6         # Compatible with FreeBSD6              
options         COMPAT_FREEBSD7         # Compatible with FreeBSD7              
options         SCSI_DELAY=5000         # Delay (in ms) before probing SCSI     
options         KTRACE                  # ktrace(1) support                     
options         STACK                   # stack(9) support                      
options         SYSVSHM                 # SYSV-style shared memory              
options         SYSVMSG                 # SYSV-style message queues             
options         SYSVSEM                 # SYSV-style semaphores                 
options         P1003_1B_SEMAPHORES     # POSIX-style semaphores                
options         _KPOSIX_PRIORITY_SCHEDULING # POSIX P1003_1B real-time extensions
options         PRINTF_BUFR_SIZE=128    # Prevent printf output being interspersed.
options         KBD_INSTALL_CDEV        # install a CDEV entry in /dev             
options         HWPMC_HOOKS             # Necessary kernel hooks for hwpmc(4)      
options         AUDIT                   # Security event auditing                  
options         MAC                     # TrustedBSD MAC Framework                 
options         FLOWTABLE               # per-cpu routing cache                    

options         HZ=1000
options         DEVICE_POLLING
options         ACCEPT_FILTER_HTTP
options         ZERO_COPY_SOCKETS 

#options        KDTRACE_HOOKS           # Kernel DTrace hooks
options         INCLUDE_CONFIG_FILE     # Include this file in kernel

# To make an SMP kernel, the next two lines are needed
options         SMP                     # Symmetric MultiProcessor Kernel
device          apic                    # I/O APIC                       

# CPU frequency control
device          cpufreq

# packet filter support
device          pf     
device          pflog  
device          pfsync 

# ALTQ support
options         ALTQ
options         ALTQ_CBQ
options         ALTQ_RED
options         ALTQ_RIO
options         ALTQ_HFSC
options         ALTQ_CDNR
options         ALTQ_PRIQ

# Bus support.
device          acpi
device          pci 

# ATA and ATAPI devices
device          ata    
device          atadisk         # ATA disk drives
device          atapicd         # ATAPI CDROM drives
options         ATA_STATIC_ID   # Static device numbering

# SCSI Controllers
device          mpt             # LSI-Logic MPT-Fusion


# SCSI peripherals
device          scbus           # SCSI bus (required for SCSI)
device          da              # Direct Access (disks)       
device          cd              # CD                          
device          pass            # Passthrough device (direct SCSI access)
device          ses             # SCSI Environmental Services (and SAF-TE)

# atkbdc0 controls both the keyboard and the PS/2 mouse
device          atkbdc          # AT keyboard controller
device          atkbd           # AT keyboard
device          psm             # PS/2 mouse

device          kbdmux          # keyboard multiplexer

device          vga             # VGA video card driver

device          splash          # Splash screen and screen saver support

# syscons is the default console driver, resembling an SCO console
device          sc

device          agp             # support several AGP chipsets

# PCI Ethernet NICs.
device          em              # Intel PRO/1000 Gigabit Ethernet Family

# Pseudo devices.
device          loop            # Network loopback
device          random          # Entropy device
device          ether           # Ethernet support
device          tun             # Packet tunnel.
device          pty             # BSD-style compatibility pseudo ttys
device          md              # Memory "disks"
device          gif             # IPv6 and IPv4 tunneling
device          faith           # IPv6-to-IPv4 relaying (translation)
device          firmware        # firmware assist module

# The `bpf' device enables the Berkeley Packet Filter.
# Be aware of the administrative consequences of enabling this!
# Note that 'bpf' is required for DHCP.
device          bpf             # Berkeley packet filter

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